Low voltage regulated power supply



1, 1956 1.. H. CRANDON ET AL LOW VOLTAGE REGULATED POWER SUPPLY FiledApril 9, 1953 FIG. 2

INVENTORS LAWRENCE H. cRAn/aonl ammo/v 5. LE) THOMAS a PRIDMOREATTORNEYS United States Patent assignors, by mesne assignments, to theUnited States of America as represented by the Secretary of the NavyApplication April 9, 1953, Serial No. 347,792

Claims. (Cl. 323'-22) This invention relates to voltage regulation withparticular application to regulation of voltages below 110 volts.

in ordinary voltage regulatory systems there is no important diflicultyin securing satisfactory regulation above 110' volts. However, belowthis voltage, as, for example, around 105 volts, difiiculties arise andit isusually necessary to build another regulated supply to serve as areference voltage. Gaseous-discharge voltage-regulator tubes: have beenused to some extent for reduced voltages but stability and regulationhave not been found satisfactory.

iln brief, the regulatory system proposed is amultistage amplifier, withthe last stage connected as a cathode foliower with 100% negativefeedback from the last stage to the first stage.

The objects of the invention are to secure adequate regulation of a lowvoltage power output, to reduce output ripple and to compensate forcathode emission changes in the control circuit.

Other objects and many of the attendant advantages of this inventionwill appear on reference to the following detailed description and theaccompanying drawings wherein:

Pig. 1 is a circuit diagram illustrating one form of the invention; and

Fig. 2 is a circuit diagram illustrating a modified form of theinvention.

In Fig. 1 the power input terminals are indicated at and 11, acrosswhich there is impressed 300 volts as received from an alternatingcurrent rectifier or other source. This voltage is closely controlled sothat the volta e divider 12 between terminals 13 and 14 on main powerlines 15 and I6 and including resistors 17' and. 18', serves as areference voltage for the system.

Tube 201s a direct coupled high gain twin triode amplitier (.l2Ax7),having an input grounded-grid triode unit 21 and output directacoupledtriode unit 22. The anode of unit 21 is connected to power main 15 viaresistor 23 and to main line 16 through resistors 24 and 25. The grid ofinput unit 21 is connected through a capacitor 26 to main line 15 andthrough resistor 27 to a point on the divider 1 2 between resistors 17and 1 8. The cathode of unit 21 is connected by conductor 28 directly tothe low potential output terminal 30. Capacitor 29 is connected betweenmain line 15 and output line 28.

The grid of output unit 22 of tube is connected. to the output of unit21 between resistors 24 and 25, and the cathode of unit 22 is connectedthrough resistor 31 to main line 15 and through resistor 32 to main line16. The anode of unit 22 joins the main line 15' through resistor 33.Cathode heaters 34 and 35 of unit cathodes are series connected, theinput triode heater 35 having a connection with the associated cathodeand the output heater being grounded.

The amplifier tube is a triode (6As7) with the anode connected to themain line 15, the cathode connected "ice 2 through resistor 41 to-mainline 16 and the grid connected to the anode of the outlet unit of tube20. The cath e is also connected from point- 42. to the low potentialoutput terminal. 30,. and thus, also, to. the cathodeof theinlet unit oftube 20, this being the well-known cathode. lower arrangement.

The operation of the circuit asset out in. Fig, 1 will now be described,assumingapplication-of a constant voltage of =3'O0 volts to main line116,. line 15 being, grounded. The capacitor and resistor constants areso. chosen that a reduced voltage of around '1IO"5 is secured atterminal 30'. Should there now be a reduction in voltage betweenterminal, 30 and ground due to load variation, the change will beimpressed on the cathode of the input unit21 of tube 20, increasing theeffective resistance of the unit and thus reducing the voltage on thegrid of the output unit. The current in the output unit 22 is thereforeincreased, increasing the output voltage as applied to the grid of tube4.0 and thereby decreasing the currentv flow in tube 40 and increasingthe negative voltage at point. 412- and at output terminal 302 Thus,there is voltage compensation for the output voltage drop. Tests haveshown: that within-v a range variation: of 5- to SO miIIiamperes theload' voltage is stabilized. within. a range of 110.01 volt. 'Also,ripple change is compensated to' within 2.5 millivoltsi If the filamentvoltage on the tubes changes, thus changing the emission'ofthe-cathodes, or if the: cathode emission changes with age, the. tubesact. asif a small voltage had. been injected in series with thecathodes. In the case of the input unit 221-. of tube 20, this injectedvoltr age will be uncompensated and will cause an equal: error voltagein the output which may exceed 0.1 volt. Where it is? desirableto'compensate for this error the-circuit diagram of Fig. 2 may beemployed. In? this circuit the same general arrangement of Fig. l isused with main lines; 15, 161 and. amplifier tube 40 connected asacathode follower to the load. However, in place of tube 20, a pair oftwin triodes- 50 and. 51 are used and: the divider and tube corn nectingcircuits are modified.

Tube 51 is substituted for the input unit 21' of tube20', the grid ofthe input grounded-grid section 5.4 havingvconnection to; a slider 53 onthe divider 52, the anode having connection to main line 15- and'thecathode having connection through resistor5 5 to main line 16*. Thecathe ode of the output section 56 of this tube is connected to theinput section cathode and. resistor 55 and both cathodes are providedwith acommon heater 57' having line connection at one end and groundconnection at the, other end. The output section grid is connectedthrough resis tor 5% to the load line 28,, and the anode is connected tothe main line 15 through resistor 23, to the grid of. input cathodefollower section: 60 of tube 50 through resistor 24 and. to main line 16through resistors 24 and 25.

The anode of the input section of tube 50 is'connected directly to themain line 15, and. the cathode is connected through resistor 32 to mainline 16 and to the cathodeof output grounded-grid section 61 ofthistube. A heater 62' is. provided for the joined cathodes, one endbeing connected to a line junction and the other to ground. The grid ofthe output section. is joined to a fixed point 83 on the divider at avoltage point lower than slider 53; and the anode is. joined throughresistor 33 tov main line 15 and to the grid of tube 40.

Examination of the circuit of Fig. 2 will show that it has acompensatory action similar to the circuit of Fig. l for all loadvoltage variations, the load voltage change being impressed on the gridof the output section 56 of tube 51 and then being transmitted throughtube 501 to tube 40 to produce a compensation for the initial, loadvariation. In addition, any change in the cathode emission, is counteredby a voltage due to the twintriode or} rangement, thus cancelling theeffect of the emission change. Thus, in tube 54 a reduction in cathodeemission results in a reduction in current flow through the tube and anincrease in plate voltage, thereby cancelling the effect of the drop incathode emission. For example, in a load variation of 3 to 20milliamperes the load voltage is stabilized within 20 millivolts, a 10percent voltage variation is held within 30 millivolts and the ripple isreduced to 1.0 millivolt.

It should be pointed out that in tubes 50 and 51 the values ofamplification and plate resistance (r for the tube units are alike andhence it amplifies the grid difference voltage like a tube with the sameresistance (rk) and, twice the internal plate resistance of a singlesection. Therefore, any voltage injected in series with the cathode,such as may in effect be due to heater current variation or diminutionin cathode emission, is reduced by the factor where n; is the commoncathode resistor.

In effect, the circuit is a super cathode follower, the amplifier unitsbeing the control grid and tube 40 being the cathode. The effective aand gm of this supercathode follower is high due to the amplification ofthe cascaded triodes inserted between the control grid and cathode. Thefluctuations of the supply voltage are accordingly reduced by n timesand the internal resistance becomes 1/ gm.

Modifications and variations of the present invention are possible inthe light of the above teachings; and it is therefore to be understoodthat within the scope of the appended claims the invention may bepracticed otherwise than as specifically described.

What is claimed is:

l. A voltage regulating system comprising: a source of D. C. voltage; afirst amplifying element having a first cathode, a first grid, and afirst plate; an output terminal; voltage dividing means for producing abias voltage which is a portion of said D. C. voltage; means forconnecting said bias voltage to said first grid; impedance means forconnecting said first plate to the positive terminal of said source ofD. C. voltage; means for connecting said first cathode to said outputterminal; a second amplifying element having a second cathode, a secondgrid, and a second plate; impedance means for connecting said firstplate to said second grid; impedance means for connecting said secondgrid to the negative terminal of said source of D. C. voltage; impedancemeans for connecting said second cathode to the positive terminal ofsaid source of D. C. voltage; impedance means for connecting said secondcathode to the negative terminal of said source of D. C. voltage;impedance means for joining said second plate to the positive terminalof said source of D. C. voltage; a third amplifying element having athird cathode, a third grid, and a third plate; leads for connectingsaid third cathode to said output terminal; impedance means forconnecting said third cathode to the negative terminal of said source ofD. C. voltage; leads for connecting said third grid to said secondplate; and leads for connecting said third plate to the positiveterminal of said source of D. C. voltage.

2. A voltage regulating system comprising: a source of D. C. voltage, afirst amplifying unit having a first positive element and a firstnegative element, means for biasing said first amplifying element with aportion of said D. C. voltage, an output terminal; means for connectingsaid first negative element to said output terminal, impedance means forconnecting said first positive element to the positive terminal of saidsource of D. C. voltage, a second amplifying unit having a secondpositive element and a second negative element, means for connecting theoutput of said first amplifying unit to the input to said secondamplifying unit, impedance means for connecting said second positiveelement to the positive terminal of said source of D. C. voltage,impedance means for connecting said second negative element to thenegative terminal and to the positive terminal of said source of D. C.voltage, a third amplifying unit having a third positive element and athird negative element, means for connecting the output of said secondamplifying unit to the input to said third amplifying unit, leads forconnecting said third positive element to the positive terminal of saidsource of D. C. voltage, leads for connecting said negative element tosaid output terminal, and impedance means for connecting said thirdnegative element to the negative terminal of said source of D. C.voltage.

3. A voltage regulating system comprising: a source of D. C. voltage, avoltage divider connected across said source of D. C. voltage, a firstamplifying unit having a first positive element and a first negativeelement, leads for connecting said first positive element to thepositive terminal of said source of D. C. voltage, impedance means forconnecting said first negative element to the negative terminal of saidsource of D. C. voltage, leads for connecting a first bias voltage fromsaid voltage divider to said first amplifying unit, a second amplifyingunit having a second positive element and a second negative element,leads for connecting said second negative element to said first negativeelement, impedance means for joining said second positive element to thepositive terminal of said source of D. C. voltage, an output terminal,impedance means for connecting any voltage on said output terminal tobias said second amplifying unit, a third amplifying unit having a thirdpositive element and a third negative element, means for connecting theoutput of said second amplifying unit to the input of said thirdamplifying unit, leads for connecting said third positive element to thepositive terminal of said source of D. C. voltage, impedance means forjoining said third negative element to the negative terminal of saidsource of D. C. voltage, a fourth amplifying unit having a fourthpositive element and a fourth negative element, leads for connectingsaid fourth negative element to said third negative element, impedancemeans for connecting said fourth positive element to the positiveterminal of said source of D. C. voltage, leads for connecting a secondbias voltage from said voltage divider to said fourth amplifying unitwhich bias is less positive than said first bias voltage, a fifthamplifying unit having a fifth positive element and a fifth negativeelement, means for connecting the output of said fourth amplifying unitto the input of said fifth amplifying unit, leads for connecting saidfifth positive element to the positive terminal of said source of D. C.voltage, leads for connecting said fifth negative element to said outputterminal, and impedance means connecting said output terminal to thenegative terminal of said source of D. C. voltage.

4. A regulator for maintaining a load voltage that is substantiallyindependent of changes in the load, said regulator comprising: a firstoutput terminal and a second output terminal, a ground connection forsaid second output terminal, a grounded-grid amplifier having a cathodedirectly joined to said first output terminals for producing a platevoltage that is a function of the voltage changes of the potentialbetween said first and second output terminals, a direct-coupledamplifier connected to amplify the plate voltage of said grounded-gridamplifier, a cathode follower circuit having a triode with a cathodedirectly connected to said first output terminal and a plate directlyconnected to said second output terminal, and leads for directlyconnecting the output of said direct-coupled amplifier to the grid ofsaid triode.

5. A regulator for maintaining a load voltage that is substantiallyindependent of changes in the load and of changes in the cathodeemission in the tubes of the regulator, said regulator comprising: twooutput terminals, 21 first tube section comprising a cathode followercircuit supplied with fixed plate and grid voltages, a second tubesection similar in physical characteristics to said first tube sectionand having a common cathode resistor with said first tube section andhaving a grid direct-coupled to one of said two output terminals forproducing an output in response to the voltage difference between gridand cathode, a third tube section comprising a cathode follower circuitdirect-coupled to be energized by the output of said second tubesection, a fourth tube section having physical characteristics similarto said third tube section and comprising a grounded-grid amplifierhaving a common cathode resistor with said third tube section forproducing an output in response to the voltage difference between gridand cathode, a cathode follower circuit having 5 follower circuit.

References Cited in the file of this patent UNITED STATES PATENTSGoldberg Jan. 6, 1948 Henley Aug. 2, 1955 OTHER REFERENCES ElectronicEngineering, September 1950, pp. 399-400.

